Phase-control of bipolar thermoelectricity in Josephson tunnel junctions

TL;DR

This paper explores how phase control influences bipolar thermoelectric effects in Josephson tunnel junctions, revealing the interplay between Josephson and quasiparticle currents and their impact on thermoelectric efficiency.

Contribution

It provides an extended analysis of Josephson contributions to thermoelectricity, demonstrating phase-independent quasiparticle thermoelectric generation and the effects of multiple thermoelectric elements.

Findings

Josephson contribution can short-circuit thermoelectric effects.

Pure quasiparticle thermoelectricity is phase-independent.

Multiple thermoelectric elements enhance output power.

Abstract

Not so long ago, thermoelectricity in superconductors was believed to be possible only by breaking explicitly the particle-hole symmetry. Recently, it has been theoretically predicted that a superconducting tunnel junction can develop bipolar thermoelectric phenomena in the presence of a large thermal gradient owing to non-equilibrium spontaneous PH symmetry breaking. The experimental realization of the first thermoelectric Josephson engine then followed. Here, we give a more extended discussion and focus on the impact of the Josephson contribution on thermoelectricity modulating the Cooper pairs transport in a double-loop SQUID. When the Cooper pairs current prevails on the quasiparticle one, the Josephson contribution short-circuits the junction thereby screening the thermoelectric effect. We demonstrate that the thermoelectric generation due to the pure quasiparticle transport is phase-independent, once Josephson contribution is appropriately removed from the net current measured. At the same time, we investigate an additional metastable state at V\simeq0 determined by the presence of the Josephson coupling, which peculiarly modifies the hysteretic behavior of our thermoelectric engine realized. At the end, we also discuss how the current-voltage characteristics are affected by the presence of multiple thermoelectric elements, which improve the generated output power.